1. Field of the Invention
The present invention relates to an improvement of a hybrid motive power vehicle comprising an electric motor and an internal combustion engine and in particular to eliminating a strange feeling during speed reduction and improving energy recovery in a hybrid motive power vehicle which performs regenerative power generation utilizing the electric motor during a speed reduction using as a load the rotation resistance of a power source.
2. Description of the Related Art
A hybrid motive power vehicle comprising an electric motor and an internal combustion engine and actuating one or both of them to drive the driving wheels is already known.
Moreover, in some of the hybrid motive power vehicles, during a speed reduction using a rotation resistance of a power source as a load, so-called engine brake, rotation of the driving wheels is transmitted via a power train system to an electric motor so as to force the electric motor to rotate, performing regenerative power generation. The electric power generated is stored in a battery so as to effectively use the energy.
However, in a case of hybrid motive power vehicle having a configuration that an electric motor and an internal combustion engine are always rotated as a unitary block, when an engine brake is actuated and the regenerative power generation is started by an electric motor, the rotation resistance by the internal combustion engine to which fuel supply has been stopped and the rotation resistance of the electric motor in regenerative power generation state function simultaneously and accordingly, the engine brake works stronger than in a normal motive power vehicle comprising only an internal combustion engine. Currently, the hybrid motive power vehicle using an electric motor and an internal combustion engine is not so popular and a driver who is accustomed to a normal motive power vehicle using only an internal combustion engine may feel a strange feeling when the engine brake of a hybrid motive power vehicle is working.
Moreover, there is a hybrid motive power vehicle having a power train clutch between the electric motor and the internal combustion engine, so that when actuating an engine brake, the power train clutch is actuated so as to disconnect the internal combustion engine from the power train system and utilize, for the engine brake, the electric motor instead of the internal combustion engine. In this case, the rotation resistance of the power source comes only from the electric motor. However, the speed reduction characteristic obtained by the internal combustion engine may be different from that of the electric motor and there is still a problem that the driver feels a strange feeling when the engine brake of a hybrid motive power vehicle is working. Moreover, because of the structure, it becomes difficult to adjust the engine brake by accelerator open degree.
It is therefore an object of the present invention to provide a hybrid motive power vehicle in which regenerative power generation is performed by an electric motor so as to effectively save the energy without causing driver a strange feeling when a speed reduction using a power source rotation resistance as a load, i.e., a so-called engine brake is actuated.
The present invention provides a hybrid motive power vehicle comprising an electric motor and an internal combustion engine, wherein during a constant speed running and an acceleration, at least one of the power sources is operated so that its drive force is transmitted to driving wheels via a power train system common to the electric motor and the internal combustion engine, and during a speed reduction using a rotation resistance of the power source as a load, rotation of the driving wheels is transmitted via the power train system to the electric motor so as to rotate the electric motor to perform a regenerative power generation, the vehicle further comprising a buffer clutch adjustable in connection force in the power train system and a buffer clutch control device for maintaining the connection force of the buffer clutch in a half-clutch state while the speed reduction is performed.
In this configuration, during a speed reduction using a rotation resistance of a power source as a load, i.e., a so-called engine braking, the buffer clutch control device operates so as to maintain a connection force of the buffer clutch in the half-clutch state. Since the buffer clutch is arranged in the power train system, even if a great rotation resistance for braking the driving wheels is generated at the upstream side of the power train system, the brake resistance actually functioning on the driving wheels is limited via the buffer clutch to a degree which can be transmitted. Accordingly, even if a great rotation resistance is generated by the rotation resistance of the internal combustion engine when the fuel supply is stopped and the rotation resistance of the electric motor in a regenerative power generation state, the force will not be directly transmitted to the driving wheels, preventing an excessive engine braking effect.
In order to obtain the engine brake characteristics of a conventional vehicle using only an internal combustion engine as a power source, the connection force of the half-clutch state of the buffer clutch is preferably set to transmit a force competing with the rotation resistance of the internal combustion engine.
Moreover, the aforementioned object can also be achieved as follows. The electric motor has an output shaft connected to an input shaft of the power train system and the vehicle further comprises: a power train clutch adjustable in connection force arranged between the output shaft of the internal combustion engine and the output shaft of the electric motor; and a power train clutch control device operating so that during a constant speed running above a predetermined speed and during an acceleration, the electric motor and the internal combustion engine are in a completely connected state via the power train clutch, and during a speed reduction using the rotation resistance of the power source as a load, the power train clutch is maintained in a half-clutch state, so that during the speed reduction the power train clutch in the half-clutch state slides so as to reduce the load of the rotation resistance given from the internal combustion engine to input shaft of the power train system while rotating the electric motor.
In this configuration, during a speed reduction using the rotation resistance of the power source as a load, i.e., engine braking, the power train clutch control device operates so as to maintain in the half-clutch state the connection force of the power train clutch connecting the output shaft of the internal combustion engine and the output shaft of the electric motor. Sliding of the power train clutch in the half-clutch state reduces the load of the rotation resistance given from the internal combustion engine to the input shaft of the power train system. The rotation resistance actually given to the input shaft of the power train system is a total of the rotation resistance of the internal combustion engine and the rotation resistance of the electric motor. Among them, the rotation resistance given from the internal combustion engine to the power train system is suppressed to a relatively low value. Accordingly, the total of the rotation resistance of the internal combustion engine and the rotation resistance of the electric motor will not cause an excessive rotation resistance functioning on the power train system, thus preventing an excessive engine braking effect.
In order to obtain the engine brake characteristic of a conventional vehicle having only an internal combustion engine as the power source, the connection force of the half-clutch state of the power train clutch is preferably set in such a manner that it is possible to transmit a force of the rotation resistance of the internal combustion engine subtracted by the rotation resistance of the electric motor, i.e., the total of the rotation resistance given to the input shaft of the power train system via the power train clutch and the rotation resistance given to the input shaft of the power train system from the electric motor is almost matched with the rotation resistance of the internal combustion engine.
Furthermore, it is also possible to simultaneously arrange the buffer clutch with the buffer clutch control device and the power train clutch with the power train clutch control device.